Critical Factors and Equilibrium Analysis of Luminescent Down‐Shifting Process for Silicon Heterojunction Solar Cells

The external quantum efficiency of silicon heterojunction (SHJ) solar cells with luminescent down-shifting (LDS) layer can be predicted by a derived equation from our optical ray model. Luminescent materials with high absorption coefficients in the blue region, large Stokes shifts, and excellent photoluminescence quantum yield are necessitated as luminescent LDSs to promote SHJ power conversion efficiency.

Abstract

Utilizing photoluminescent quantum dots (QDs) as a luminescent down-shifting (LDS) layer to convert high-energy photons into lower-energy ones is a prominent approach to reducing parasitic absorption of silicon heterojunction (SHJ) solar cells. Here, a ray-optic model is presented to gain insight into light conversion contribution on the short-circuit current density (J_sc ) of the SHJ solar cell with an LDS layer. The correlation reveals that the primary factors impacting external quantum efficiency (EQE) are the absorption coefficient at short wavelengths and the photoluminescence quantum yield (PLQY) of the LDS layer. Notably, PLQY is dominant in determining the contribution to the device efficiency if the LDS layer can harvest all the parasitic light, particularly when there is no surface reflectance change. Furthermore, the EQE spectrum of high-efficiency SHJ solar cells is experimentally investigated with the QDs LDS layer to validate the model, revealing that it aligns well with the experiment results. Employing a MgF₂/QDs LDS layer, the J_sc with 0.50 mA cm^{− 2} is enhanced, yielding the SHJ solar cells with an efficiency of over 22.3%. The work develops a broadly applicable model that aids in screening suitable photoluminescent materials for LDS layer applications in photovoltaic devices and elucidates the theoretical contributions to EQE.